What does axis-aligned mean?

Question

What does axis-aligned mean. For example when you get a bounding rectangle of a geometry it says:

Gets a Rect that specifies the axis-aligned bounding box of the Geometry.

What does axis-aligned mean, and what axis is it aligned to, the containing panel/element parent or the window?

Answer 1

It means that the rectangle isn't rotated at all, its edges follow the X and Y axes.